excess blood in right ventricle

my son had a fainting episode after playing hockey..  the cardiologist found that he has left svc and also too much blood in the right ventricle.. The echo showed no defect, valve problem or any other reason for the excess blood..  he is getting an mri but wanted some info on what may cause this... Would a septial defect show up on an echo?  He is 13 and has always been healthy..

[Marie M Gleason, M.D.]

Dear hockeymom8:  Fainting after exercise is not uncommon in some growing children.  They may have a rapid drop in blood pressure and heart rate as they slow their activities, leading to dizziness or fainting.  This is generally benign, but definitely worth getting an evaluation by a pediatric cardiologist.   There are several reasons why the right side of the heart could be enlarged on a echocardiogram.  The most common cause is an atrial septal defect (ASD).  The most common spot for these holes is in the mid-portion of the atrial wall,  and these are generally found on transthoracic echocardiograms if the imaging windows are reasonable. There are ASD locations that may be harder to visualize by echocardiography.  These are called sinus venosus ASDs and can be located very high or very low along the atrial wall where the large veins enter the heart.  Another cause is partially anomalous pulmonary venous return (PAPVR).  There are sets of veins from the right and left lungs that connect to the left atrium bringing the oxygenated blood to the heart, so it can be pumped to the body.  In PAPVR,  some (not all) of the pulmonary veins can connect to other areas, such as the right atrium, coronary sinus or other draining veins.  The result is extra blood returning to the right sided heart chambers, which then enlarge over time.   Another cause is severe tricuspid valve leakage.  This valve separates the right atrium and right ventricle from each other, and, if leaking significantly, should have been picked up by the echocardiogram.  Lastly, if the pressures in the lungs are elevated (pulmonary hypertension), this can enlarge the right sided  heart chambers.  It can also cause people to pass out.  However, your son’s physical examination and electrocardiogram (ECG) would be abnormal if this was the case.  A cardiac MRI is a good tool for evaluating the pulmonary venous return (PAPVR) and also for finding sinus venosus atrial septal defects.  These types of congenital heart disease would require open heart surgery to fix.  Some of the ASDs in the mid-septum, called secundum ASDs, may be closed by devices in the cardiac catheterization laboratory.  Good luck.